Architectural Fabric

ABSTRACT

An article useful as an architectural fabric consisting of (a) a layer of fabric having a first surface and a second surface made of polytetrafluoroethylene fibers; and (b) a fluoropolymer coating disposed on at least the first surface of the fabric.

RELATED APPLICATION

The present application is a divisional application of pending U.S.patent application Ser. No. 11/195,911 filed Aug. 2, 2005.

FIELD OF INVENTION

The present invention relates to fabric and, more particularly, toarchitectural fabric that is waterproof, fire retardant, flexible,durable, and aesthetically pleasing.

BACKGROUND OF INVENTION

Architectural fabric is fabric used as a building structure or part of abuilding structure. It typically provides protection for humans fromelements such as wind, sun, and rain. It may be a permanent structure ora temporary one. If temporary, it may be retractable or removable, forexample by folding, rolling, or otherwise storing.

There are several requirements for architectural fabric. It must bestrong enough to withstand wind and other stresses during assembly anduse. It must be flexible and durable, so that it can be folded or rolledand its strength and integrity are maintained over time. It must be UVlight resistant. UV light tends to degrade and weaken fabric over time.A fabric that is UV resistant will stand up under this exposure. Itshould generally be fire retardant and waterproof. It should be easilyseamed (or “welded”). It must also be aesthetically pleasing.

A known architectural fabric is a composite consisting of fiberglassfabric coated with PTFE. Although this product has certain desirablequalities, it is not suitably flexible. The fabric thus cannot be usedefficiently in applications where convenient removal of the fabric isneeded.

Another known architectural fabric has a coating of PVC or acrylic onpolyester fabric. These products have flexibility but only limiteddurability. Unless specially treated, these fabrics are flammable andtend to degrade under UV light. After a certain amount of flexing and UVexposure, these products develop cracks or other imperfections thatallow water to penetrate the fabric at the point where it has beencompromised.

Another known architectural fabric is that disclosed in U.S. Pat. No.6,770,577B2 to Kelmartin et al. The article disclosed therein comprisesa polytetrafluoroethylene fabric attached to at least one compositemembrane of a porous polytetrafluoroethylene film having a fluoropolymeradhesive (such as THV) contained in its pores. The porouspolytetrafluoroethylene film is provided to make the article durable andaesthetically pleasing. Addition of the film requires additionalprocessing, however. The film also tends to mute any pigments or colorsin the fabric or the THV.

An economical, weldable, waterproof, fire retardant architectural fabricis needed in the industry.

SUMMARY OF INVENTION

The present invention provides an article consisting of (a) a Layer offabric having a first surface and a second surface made ofpolytetrafluoroethylene fibers; and (b) a fluoropolymer coating disposedon said first surface of said fabric. In another embodiment, theinvention further includes a fluoropolymer coating disposed on thesecond surface of the fabric. The fluoropolymer coating is preferablyTHV. The article of the present invention is preferably waterproof, fireretardant, and has high seam strength. It is also preferably anarchitectural fabric for retractable, temporary, or permanentstructures, such as tensile structures, and is adapted to be joined toitself by welding.

In another aspect, the present invention provides a method of making anarchitectural fabric for a retractable, temporary, or permanentstructure by:

-   -   (a) providing a layer of fabric having a first surface and a        second surface and comprising polytetrafluoroethylene fibers;    -   (b) disposing THV on the first surface of said fabric; and    -   (c) optionally disposing THV on the second surface of said        fabric.

In another aspect, the invention provides a method of making anarchitectural fabric comprising the steps of

-   -   (a) providing a fluoropolymer fabric    -   (b) extrusion coating the fluoropolymer fabric with THV by        simultaneously extruding the THV onto the fabric and nipping the        fabric and extruded THV between a first roll and a second roll.

BRIEF DESCRIPTION OF INVENTION

FIG. 1 is an optical micrograph of a cross-section of an article inaccordance with an exemplary embodiment of the present invention.

FIG. 2 is a schematic illustration of an exemplary process for making anarticle according to the present invention.

DETAILED DESCRIPTION OF INVENTION

The present invention will now be described with reference to thefigures in the drawing. FIG. 1 is an optical micrograph of across-section of an article 10 according to an exemplary embodiment ofthe present invention. In this exemplary embodiment, article 10 is anarchitectural fabric. Article 10 includes a fabric 11 made of fibers 13of a fluoropolymer material, preferably PTFE fibers that have sufficientstrength for a particular application, and most preferably expanded PTFEfibers. Fabric 11 has a warp and a weft direction, accounting for thecross-sectional views perpendicular to and parallel to the axes of theindividual fibers of fabric 11 shown in FIG. 1.

Fabric 11 has a first surface 20 and a second surface 21. Disposedadjacent to first surface 20, which extends along fibers 13 in both thewarp and weft direction, and extending in between and among fibers 13 isa fluoropolymer coating 12, preferably a terpolymer oftetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (THV).

Article 10 is useful as an architectural fabric with only first surface20 covered by fluoropolymer coating 12. A preferable embodiment,however, also has fluoropolymer coating 12 disposed on second surface 21(and extending between and among fibers 13 from such second surface 21).

Fabric 11 is any material that is UV light resistant and fire retardant.It must also be strong, flexible and durable. PTFE fiber is preferred.Fabric made from expanded polytetrafluoroethylene fibers is mostpreferred.

Fluoropolymer coating 12 is a material that is UV light resistant andfire retardant. THV is preferred. This preferred fluoropolymer coatingis also advantageously flexible, adherent to the fabric 11 (withoutbeing limited by theory, it is believed that the THV is able toencapsulate the fibers of fabric 11 to form a mechanical bond ratherthan a chemical bond) and clear or translucent. Preferably, the coatingon both sides of the fabric is the same material. THV can be filled forfunctionality, such as color, UV resistance (if needed, for example ifno PTFE fabric is used), and flame resistance.

Fluoropolymer coating 12 is preferably applied to fabric 11 by extrusioncoating, although other methods, such as solvent coating or laminationwith or without the use of release layers are alternatives. FIG. 2depicts a preferred extrusion coating process for making thearchitectural fabric of this invention. Fabric 11 is passed betweenrolls 91 and 92 while fluoropolymer coating 12 is simultaneouslyextruded onto fabric 11 from extruder 90. The surfaces of rolls 91 and92, as well as the temperature and speed of the rolls are criticalprocessing parameters for making the present invention. Details of theseparameters are given in the example below.

Surprisingly, Applicant has discovered that the article of the presentinvention functions well as an architectural fabric. Contrary to theconventional wisdom expressed in U.S. Pat. No. 6,770,577B2 to Kelmartinet al., Applicant has discovered that an architectural fabric madewithout the PTFE film disclosed in Kelmartin is durable, processable andaesthetically pleasing. As stated in this patent, “[w]hen THV alone isused to coat the fabric, the surface has a blotchy appearance that istacky. With the inventive article, however, the surface appears uniformand is not tacky. This also provides unexpected improvements inprocessability. The article does not stick to or coat processing rollsduring manufacture.” It was thus conventional wisdom before the presentinvention that elimination of the porous polytetrafluoroethylene filmwould be undesirable.

Also surprisingly, article 10 can be much more easily seam-sealed toitself using welding techniques known in the art of seam-sealing forexample, with PTFE/fiberglass fabrics. This is a result of theelimination of the microporous PTFE element described in U.S. Pat. No.6,770,577B2. A variety of seaming techniques can be used. A secure seamis formed by applying heat (about 230 degrees C. for 45 seconds) andpressure to overlapped portions of the inventive fabric. A suitable seamsealing device is an electric impulse hot bar welder available fromAline Heat Sealing Corporation, Cerritos Calif., part number HD-25.Surprisingly, radio frequency welding can also be used, as can wedgewelding and hot-air welding. Using the invention, one can easily get astrong weld without the need for special processing, or for addingadditional adhesives or seam tape as with other fabrics currently used.

The following example is intended to illustrate, but not limit, thepresent invention.

EXAMPLE An architectural Fabric was Prepared as Follows

THV220 (Dyneon, Inc, Oakdale, Minn.) which was pigmented tan wasextruded using a single screw extruder and a slotted die at atemperature of 250 C. It was directed vertically downward into a nipcreated by two rolls; one being a TEFLON®-sleeved EPDM rubber roll andthe other a TEFLON®-coated steel roll. The thickness of the extrudedfilm was 175 micrometers. The EPDM roll had a surface temperature of 90C, and the steel roll had a surface temperature of 115 C. The surfacespeed of the rolls was 2.75 meters per minute. Fabric woven of expandedPTFE fiber was obtained from W.L. Gore & Associates, Inc. This fabricwas woven in a plain weave, 18 ends by 18 picks per centimeter. Each endand each pick yarn was composed of two 500 denier expanded PTFE fibersplied together.

The fabric entered the nip over the steel roll and was pressed againstthe molten THV220 in the nip. The nip force was 130 Newtons percentimeter. The THV220 was pushed into the voids in the fabric by theaction of the nip. The resulting THV220/fabric composite was wound ontoa roll at the end of the extrusion line.

The aforementioned THV220/fabric composite was then run a second time onthe extrusion line except that a second coating of molten THV220pigmented red was applied to the fabric face which was not extruded uponin the first pass. The machine conditions were the same for this secondpass as they were for the first pass. This material produced in thisexample was identified as 360-75. The thickness of the THV220/fabriccomposite was 0.65 millimeters, and the mass per unit area was 1240grams per square meter.

TESTING

The fabric produced according to the above example was tested forvarious properties as follows.

(1) Waterproofness

Apparatus:

RO/Distilled water

Thermometer

Low Hydrostatic Pressure Tester (Alfred Suter Co., Ramsey, N.J., ModelNo. 502 Suter LHPT)

Timer

Water Circulator

Test Specimens:

Specimen size: circular sample of 4½″ (11.4 cm) diameter.

Specimens per sample: Three.

Conditioning: Condition the specimens at 21±1° C. (70±2° F.), 65±2% RHprior to testing.

Test Procedure:

-   1. Check the water level in the tank.-   2. Add water if the level is too low.-   3. Turn the pump on.-   4. Check that the water temperature is at 27±3° C. (80±5° F.).    -   4.1 Run the motor to heat or add heated water to the tank if the        water temperature is too low.    -   4.2 Float an ice pack, located in the freezer, in the tank to        lower the temperature if the water temperature is too high (or        becomes too high while testing), or add cold water.-   5. Purge the water lines.-   6. Place a specimen face side down under the specimen holder.-   7. Clamp the specimen in place.-   8. Open the valves to start water flow.-   9. Set a timer for 3 minutes.-   10. Start the timer when the gauge on the LPHT tester reaches the    specified pressure (1.1 psig).-   11. Check each specimen for leaks, Samples that leak are reported as    failures. Those that do not leak, pass.    -   11.1 Failures should only be counted if leaks occur in the test        area.        -   11.1.1 Drops of water penetrating the specimen at the            clamped edge of the specimen or within 0.32 cm (⅛″) of this            edge shall not be counted.

Three samples of the example material were tested as described above.All three samples passed with no leakage.

(2) Fire Retardance

The example fabric was tested for fire retardance as follows.

Apparatus:

Cabinet including Tirrill Burner Brass weights Metal specimen holder andclips Scissors or hole punch Specimen mounting block Butane lighterTimer (tenths of seconds) Disposable gloves Metric ruler (1 mmgraduations) Gas: methane 99% pure Plastic bag

Test Specimens:

-   -   Specimen size: 3″×12″ with the 12″ length parallel to the test        direction. Number of samples: two.    -   Conditioning: Condition the specimens at 70±2° F., 65±2% RH        prior to testing.

Test Procedure:

1. Cut specimens as specified above.

-   -   1.1. Ensure that the gas pressure is 2.5±0.25 psi.    -   1.2. Turn power on (control panel on counter).    -   1.3. Turn the pilot knob slightly counter-clockwise, so that it        is on.    -   1.4. Ignite the pilot with the butane lighter.    -   1.5. Adjust the pilot size to ⅛″ using the pilot knob. Measure        the pilot flame from its lowest point to the tip.    -   1.6. Set the flame ignition timer to 120 seconds.    -   1.7. Turn the flame/fan knob to flame and burn the flame for at        least 2 minutes prior to the beginning of each set up and        testing session,    -   1.9. Adjust the flame height to 1.5″ by turning the knob at the        bottom of the burner clockwise to increase the height or counter        clockwise to decrease the height. The tip of the flame should        reach the top point of the flame indicator.    -   1.10. Re-set the flame ignition timer to 12 seconds and re-light        the flame.    -   1.11. Turn the flame/fan knob to fan.    -   1.12. Place the metal specimen holder on the mounting block.    -   1.13. Align a dummy specimen in the metal holder with the short        edge of the dummy aligned with the lower edge of the holder.    -   1.14. Close the specimen holder and clamp with the clips at two        places on each side making sure the dummy is smooth and flat in        the holder.    -   1.15. Turn the flame/fan knob to flame.    -   1.16. Light the flame with the butane lighter.    -   1.17. Immediately turn the flame/fan knob to off.    -   1.18. Position the specimen holder securely in the cabinet.    -   1.19. Make sure the holder is positioned in the groove of the        holder rest at the back of the cabinet and the middle of the        lower edge of the specimen is centered ¾″ above the burner.    -   1.20. Close the cabinet door and the hood sash.        -   Note: The specimen must be tested within 2 minutes of being            placed in the cabinet.    -   1.21. Turn the flame/fan knob to flame to start the 12-second        flame.    -   1.22. Once the 12-second flame has extinguished confirm that the        pilot light is the proper size.    -   1.23. Depress the door release button and allow the cabinet to        ventilate for 30 seconds or until all smoke and fumes are        removed.    -   1.24. Adjust the pilot light, if necessary, and repeat steps        1.15 through 1.24 as needed until proper pilot size is        maintained.

2. Testing:

-   -   2.1. Place the metal specimen holder on the mounting block.    -   2.2. Align the specimen in the metal holder such that the test        area does not contain any identification markings when the short        edge of the specimen is aligned with the lower edge of the        holder.    -   2.3. Close the specimen holder and clamp with clips at two        places on each side making sure the specimen is smooth and flat        in the holder.    -   2.4. Turn the flame/fan knob to flame.    -   2.5. Light the flame with the butane lighter.    -   2.6. Immediately turn the flame/fan knob to off.    -   2.7. Position the specimen holder securely in the cabinet.    -   2.8. Make sure that the holder is positioned in the groove of        the holder rest at the back of the cabinet and that the middle        of the lower edge of the specimen is centered ¾″ above the        burner.    -   2.9. Close the cabinet door and the hood,    -   Note: The specimens must be tested within 2 minutes of being        place in the cabinet.    -   2.10. Turn the flame/fan knob to flame to start the 12-second        flame.    -   2.11. Determine the after-flame, and after-glow time, and the        presence of melting or dripping, after the 12-second flame        extinguishes, and record in the lab database.        -   2.11.1. After-flame: Using the timer mounted on the hood,            measure the number of seconds, to the nearest 0.1 seconds,            that the material continues to burn after the igniting flame            extinguishes. Do not turn the fan on until the specimen has            stopped glowing, regardless of whether or not the after-glow            is being measured.        -   2.11.2. After-glow: Using the automatic timer, measure the            number of seconds, to the nearest 0.1 seconds, that the            material glows after the flaming ends. The glow shall not be            extinguished even if after-glow time is not being evaluated            because of the glow's effect on char length.        -   2.11.3. Melt/Drip: Look for signs of melting or dripping.    -   The example material tested for fire retardance had the        following results, illustrating that the material was indeed        fire retardant.

Sample:360-75

Standard A B C Average Deviation Warp Afterflame(sec) 1.3 1.2 1.2 1.230.05 Afterglow(sec) 0 0 0 0.00 0.00 Melt/Drip Melt/ Melt/ Melt/ No DripNo Drip No Drip Char 1.4 1.55 1.85 1.60 0.19 Length(cm) FillAfterflame(sec) 1.2 1.1 1 1.10 0.08 Afterglow(sec) 0 0 0 0.00 0.00Melt/Drip Melt/ Melt/ Melt/ No Drip No Drip No Drip Char 1.6 1.45 1.851.63 0.16 Length(cm)

(3) Seam Strength

Two pieces of the example fabric were placed in overlapping relationshipin the warp direction, such that 2.5 inches (6.35 cm) of each pieceoverlapped. No seam tape was used, nor was any scuffing or abrasionperformed on the areas to be welded. The overlap was welded to form aseam with an Aline Welder Model HD-25 at 230 degrees C. for 45 seconds.Strips of the fabric were cut 2 inches (5.08 cm) wide by 14 inches (35.5cm) long with the long direction perpendicular to the seam. The seamstrength was tested by pulling the seam on a tensile tester (InstronCorporation, Norwood Mass., Model 5567) with 4 inch (10.16 cm) gaugelength at 2 inches (5.08 cm) per minute extension rate. Five suchspecimens were produced. The results are tabulated below, and indicate avery strong seam was produced using this simple welding technique on theinventive fabric. A seam having a strength of at least 90% of thenominal strength of the fabric is desired.

Percent of Nominal Fabric Strength Max Force Max Force Max Force (456Lb/in-4000 N/ Specimen (Lb/2 Inch) (Lb/Inch) (N/5 cm) 5 cm) 1 929 4654074 102% 2 901 451 3951 99% 3 868 434 3806 95% 4 884 442 3876 97% 5 882441 3868 97% Average 893 446 3915 98% Std. Dev. 23.4 11.7 102.5 COV 2.6%2.6% 2.6%

While particular embodiments of the present invention have beenillustrated and described herein, the present invention should not belimited to such illustrations and descriptions. It should be apparentthat the changes and modifications may be incorporated and embodied aspart of the present invention within the scope of the following claims.

1. A method of making an architectural fabric comprising the steps of(a) providing a fluoropolymer fabric having a first surface and a secondsurface, and (b) extrusion coating the first surface of saidfluoropolymer fabric with THV by simultaneously extruding the THV ontothe fabric and nipping the fabric and extruded THV between a first rolland a second roll.
 2. A method of making an architectural fabric asdefined in claim 1 further comprising the step of extrusion coating thesecond surface of said fluoropolymer fabric with THV by simultaneouslyextruding the THV onto the fabric and nipping the fabric and extrudedTHV between a first roll and a second roll.
 3. A method of making anarchitectural fabric for a retractable, temporary, or permanentstructure comprising the steps of: (a) providing a layer of fabrichaving a first surface and a second surface and comprisingpolytetrafluoroethylene fibers; (b) coating THV onto said first surfaceof said fabric; and (c) coating THV onto said second surface of saidfabric.